Recently, as various portable electronic devices such as mobile phones, PDAs, and laptop computers have been developed, the requirement for light, slight, and small flat panel displays applicable to the portable electronic devices is gradually increased. In this regard, the flat panel displays such as liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs) have been actually studied and commercialized recently.
Metallic wiring patterns provided inside the devices or color filter patterns in the LCD have been realized through various schemes of forming patterns, such as a screen printing scheme and a photolithography scheme. However, according to the screen printing scheme, the patterns are formed with low precision. According to the photolithography scheme, processes are complicated in that the photoresist must be laminated, exposed, and developed. Accordingly, the schemes have the limitation in forming micro-patterns.
In other words, the wiring electrode of the touch panel according to the related art is generally formed through the photolithography scheme. The photolithography is a kind of photo process including a coating process of a photoresist, a mask alignment process, an exposure process, a developing process, and a stripping process. The photolithography takes the long process time, wastes a great amount of strip solution to remove photoresist and a photoresist pattern, and requires high-price equipment such as exposure equipment.
In particular, the photolithography has disadvantages in that the price of the exposure equipment is increased, and the control of the pitch precision and an electrode width is difficult as the size of a substrate is enlarged and a pattern size is reduced.
Accordingly, as the substitute for the photolithography, a gravure offset printing scheme employing a blanket for printing has been developed. Since the gravure offset printing scheme may make a line pattern thin, the gravure offset printing scheme has been spotlighted as the substitute for the photolithography.
The gravure offset printing scheme is a printing scheme used in forming the electrodes of the flat panel displays by using an intaglio scheme and/or a relief scheme and the transfer characteristic of ink. In general, the offset printing scheme is classified into two processes of an off process and a set process. Before the off process is performed, a paste composition is filled in a printing roll having a pattern with micro-line width and depth, and then a doctoring process to strip off composition flowed over the printing roll is performed. Thereafter, according to the off process, a blanket roll and the printing roll filled with the composition are continuously pressurized with respect to each other while rotating, so that the composition filled in the groove of the printing roll is transferred to a silicon-rubber surface of the blanket roll. In addition, according to the set process, the blanket having a silicon-rubber surface and a glass plate are pressurized with respect to each other while rotating, so that the composition transferred onto the silicon surface of the blanket is transferred onto the glass plate again.
In order to print a micro-pattern through the offset printing scheme, the paste must be sufficiently filled in the gravure pattern, and must be neatly transferred to the blanket due to the superior matching with the blanket.
In particular, in order to print a micro-pattern of 50 μm or less, the paste must include metallic micro-particles of 5 μm or less, and must be excellently dispersed. However, the acryl-based dispersing agents according to the related art represent the lower solubility with respect to an ether solvent and thus cause the problems related to the adhesive strength.
In order to solve the above problems, a paste composition for printing capable of facilitating an inking work by improving particle dispersibility is required.